In LTE, Long Term Evolution, a User Equipment needs to identify and measure inter-frequency and/or inter-RAT (Radio Access Technology) cells in order to support mobility or Automatic Neighbor Related, ANR, functions. ANR functions belong to Self-Optimizing Network, SON, functions. An example is to automatically find neighbor relations and/or neighbor cells. In order to perform the identification and the measurements, the User Equipment (UE) requires measurement gaps during which the UE may perform these actions.
During these measurement gaps, the UE is not allowed to transmit or receive any data and/or to tune its receiver on the Evolved Universal Terrestrial Radio access Network, E-UTRAN, serving carrier frequency based on the UE's own capability.
The base station, or evolved Node B (eNB), provides the UE with a measurement configuration, which is specified by a Measurement Gap Length, MGL, and a Measurement Gap Repetition Period, MGRP. During a measurement gap, the UE is not allowed to transmit or to receive signals on the serving carrier.
Within each MGRP, a measurement gap starts at a System Frame Number (SFN) and subframe. The time from the beginning of the MGRP to the beginning of the measurement gap is referred to as a gap offset.
In LTE, Hybrid Automatic Repeat Request, HARQ, transmissions follow certain timing sequences, and different HARQ processes or transmissions run simultaneously with different HARQ starting subframes. In Frequency Division Duplex, FDD, mode, the timing sequence of downlink and uplink HARQ transmission is the same for different starting subframes, i.e. for downlink HARQ timing, the uplink acknowledgement, ACK, and/or negative acknowledgement, NACK, timing delay is the same for Packet Data Control Channel, PDCCH, and Physical Downlink Shared Channel, PDSCH, transmission in different subframes. Likewise, for uplink HARQ timing, the Physical Uplink Shared Channel, PUSCH, delay and the Physical Hybrid ARQ Indicator Channel, PHICH, delay are the same for PDCCH grant and/or PHICH ACK/NACK in different subframes. As a consequence, different gap offsets have the same impact on data interruption for downlink and uplink HARQ transmissions, provided that the MGL is the same.
However, in Time Division Duplex, TDD, mode, the delays are different for different uplink and downlink configurations or different HARQ starting subframes of the same uplink/downlink configuration. As a consequence, different gap offsets have different impact on data interruption. As a consequence, there is a problem that data transmission may be interrupted to a substantial extent.